1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus and a chemical vapor deposition method. More particularly, it pertains to a chemical vapor deposition apparatus wherein a gas containing a feed gas is introduced at a gas introduction portion of a horizontal tubular reactor which is arranged such that the direction of the feed gas to be fed in the reactor is made substantially parallel to a substrate, so that uniform semiconductor films with favorable crystallinity are subjected to chemical vapor deposition in high efficiency on a heated substrate; and to a chemical vapor deposition method by using the aforesaid apparatus.
2. Description of the Related Arts
There has been a rapid increase in recent years, in demands for a gallium nitride compound semiconductor to be used as a device for a light emitting diode, laser diode, and the like concentratedly in the field of optical communication. There is known, for instance, as a process for manufacturing a gallium nitride compound semiconductor, a process in which a semiconductor film of a gallium nitride based compound is subjected to chemical vapor deposition on a substrate of sapphire or the like which has been set in advance in a tubular reactor so as to form an objective film by using, as a group m metal source, an organometallic gas such as trimethylgallium, trimethylindium and trimethylaluminum and by using ammonia as a nitrogen source.
In addition, there is available, as an apparatus for manufacturing the above-mentioned gallium nitride compound semiconductor, a chemical vapor deposition apparatus comprising a horizontal tubular reactor equipped with a susceptor for mounting a substrate thereon, a heater for heating the substrate, a feed gas introduction portion arranged such that the direction of the feed gas fed in a tubular reactor is made parallel to the substrate, and a reaction gas exhaust portion. The chemical vapor deposition apparatus comprising the horizontal tubular reactor is of such constitution that the substrate is placed on the susceptor in the tubular reactor, the substrate is heated, and thereafter a gas containing a feed gas is supplied in the reactor in the direction parallel to the substrate so that a semiconductor film is subjected to chemical vapor deposition to form a film on the substrate.
However, in such a horizontal tubular reactor, since the feed gas is diffused by the thermal convection in the vicinity of the substrate and does not efficiently reach the substrate, there is caused such a problem that uniform semiconductor films with favorable crystallinity are unobtainable, or the growth rate of films is low.
However, there have recently been developed an improved apparatus and method for chemical vapor deposition wherein a forcing gas introduction portion is placed on the tubular reactor wall in opposition to the substrate, a forcing gas not affecting the reaction of a carrier gas and the like is supplied inside the tubular reactor in the direction perpendicular to the substrate so as to change the feed gas stream to the direction of spraying it to a substrate. It is said that the improved apparatus and method enable to obtain uniform semiconductor films with favorable crystallinity by properly and optionally controlling the flow rate of the forcing gas in accordance with the kind and flow rate of the feed gas, temperature of the heated substrate and the like.
Nevertheless, with regard to the aforesaid method and apparatus, gas streams which cross at right angles, that is, a gas containing the feed gas and the forcing gas are mixed with each other on the substrate, and thus are more prone to be disordered, whereby the streams are often difficult to control. For instance, in the case of effecting chemical vapor deposition of a large-size substrate or simultaneously conducting that of a plurality of substrates, it is difficult to supply a feed gas in uniform concentration over a wide range of a substrate. Moreover in the case of conducting chemical vapor deposition by using the foregoing trimethylgallium, trimethylindium or trimethylaluminum as a feed gas, the necessity for a high temperature of 1000xc2x0 C. or higher as the substrate heating temperature makes it difficult to control the intricate gas streams on the substrate.
Under such circumstances, an object of the invention is to provide a method and an apparatus for chemical vapor deposition that are capable of subjecting uniform semiconductor films with favorable crystallinity to chemical vapor deposition in high efficiency on a heated substrate in using a horizontal tubular reactor even in the case of conducting chemical vapor deposition of a large-sized substrate or simultaneously performing that of a plurality of substrates, or performing the same at a high vapor deposition temperature.
Other objects of the invention will become obvious from the text of this specification hereinafter disclosed. In such circumstances, intensive extensive research and development were accumulated by the present inventors in order to solve the above-described problems involved in the prior arts. As a result, it has been found that in regard to chemical vapor deposition using a horizontal tubular reactor, the feed gas stream can be changed to the direction of spraying it onto the substrate without supplying a forcing gas by installing on a tubular reactor wall in opposition to the substrate, an inclined portion inclining downward from the upstream side of the feed gas passageway towards the downstream side thereof.
It has also been found that in regard to chemical vapor deposition using a horizontal tubular reactor, disorder of the gas stream or diffusion of a feed gas each due to the thermal convection in the vicinity of the substrate can be suppressed by such a constitution that the spacing between a susceptor and a tubular reactor wall in opposition thereto is made smaller than the vertical spacing in the tubular reactor wall between a feed gas introduction portion and the susceptor. The present invention has been accomplished by the above-mentioned findings and information.
That is to say, the present invention relates to a chemical vapor deposition apparatus for a semiconductor film, which comprises a horizontal tubular reactor equipped with a susceptor for mounting a substrate thereon, a heater for heating the substrate, a feed gas introduction portion arranged such that the direction of a feed gas supplied in the tubular reactor is made substantially parallel to the substrate and a reaction gas exhaust portion, wherein the constitution of the apparatus is such that part of the tubular reactor walls in opposition to a substrate inclines downward from the upstream side of the feed gas passageway towards the downstream side thereof.
In addition, the present invention is concerned with a chemical vapor deposition method which comprises mounting a substrate on a susceptor in a horizontal tubular reactor, heating the substrate with a heater, and supplying the substrate with a gas containing a feed gas in the direction substantially parallel to the substrate so as to subject a semiconductor film to chemical vapor deposition on said substrate, wherein the direction of the gas stream is changed to an oblique downward direction by such a constitution that part of the tubular reactor walls in opposition to a substrate inclines downward from the upstream side of the feed gas passageway towards the downstream side thereof.
Moreover, the present invention pertains to a chemical vapor deposition apparatus for a semiconductor film, which comprises a horizontal tubular reactor equipped with a susceptor for mounting a substrate thereon, a heater for heating the substrate, a feed gas introduction portion arranged such that the direction of a feed gas supplied in the tubular reactor is made substantially parallel to the substrate, and a reaction gas exhaust portion, wherein the constitution of the apparatus is such that the spacing between the susceptor and the tubular reactor wall in opposition thereto is made smaller than the vertical spacing in the tubular reactor wall from a gas feed port in the feed gas introduction portion to the upstream side end of the feed gas passageway for the susceptor.
Further, the present invention is related to a chemical vapor deposition method which comprises mounting a substrate on a susceptor in a horizontal tubular reactor, heating the substrate with a heater, and supplying the substrate with a gas containing a feed gas in the direction substantially parallel to the substrate so as to subject a semiconductor film to chemical vapor deposition on said substrate, wherein the gas containing a feed gas is supplied into the horizontal tubular reactor having such a constitution that the spacing between the susceptor and the tubular reactor wall in opposition thereto is made smaller than the vertical spacing in the tubular reactor wall from a gas feed port in the feed gas introduction portion to the upstream side end of the feed gas passageway for the susceptor.